Electrodynamic telephone



June 12, 1934 H. NNNNN NN 1,962,206

EEEEEEEEEEEEEEEEEEEEE NE NNNNNN OR AAAAAAAAA NN fil Patnied June 12, 1934 UNITED STTES ELECTRODYNAMIC TELEPHONE Hans Neumann, Berlin-Siemensstadt, Germany, assignor to Siemens & Halske, Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany Application April 5, 1932, Serial No. 603,334 In Germany May 9, 1931 2 Claims.

The invention is concerned with electrodynamic telephones of the kind which are safe guarded against short-circuiting between the conductors carrying the voice currents and the poles of the magnet system. In these telephones the conductors attached to the diaphragm and carrying the voice currents project into the narrow air gaps of the magnet system which, for instance, may be Constructed grate-fashion. For the purpose of precluding such short circuits as may arise under service conditions between conductors and poles it has been Suggested to cover the latter at the ends located opposite the conductors, with a thin insulating coat. The insulating coat is protected against damage by the oscillating conductor by magnetic metal pieces fitted thereon.

As has been found from practical experience, rather high field intensities arise between the poles, say, up to 25,000 Gauss. Owing to the appreciable mechanical tensile forces thus oceasioned, the metallic pieces provided for protection of the insulation coat are torn olf. This seriously disturbs the Operation of the teleplione. Because of the little space available in the air gap (amounting some times to as little as 11/2 to 2 mm), it is very hard to secure the metallic protector pieces in place.

According to the present invention metallic magnetic pieces are fitted on and insulated from the pole pieces. They are united With the pole pieces in form-fit fashion in the direction of the mechanical tensile forces that will arise.

For instance, the said metallic pieces may be furnished with extensions or lugs projecting at right angles to the mechanical pulls and fitted or inserted into suitable slots in the pole pieces. The formation of the said lugs or projections may be chosen at will; e. g., they may be dove-tailed. The metal pieces, if desired, could constitute also parts of the pole shoes or may form the latter.

The invention is described in more detail by the aid of the embodiment illustrated, by way of example, in the attached drawing. Attached to the diaphragm 1 are the conductors 2 carrying the voice currents. These conductors oscillate inside the air gap 4 formed by the pole pieces 3. The conductors are insulated from the pole pieces 3 by means of the thin insulation layers 5 which consist, for example, of pressed insulation material of 0.1 mm. thickness so as to prevent shortcircuiting and protected by means of the metallic pieces 6 which are snugly fitted thereto. These metallic pieces 6 are provided with projecticns 8 extending at right angles to the direction of the mechanical pulls that are set up. These projections 8 are firmly fitted into suitable slots 9 in the pole pieces 5. In addition, the metal pieces are united with the pole pieces by the aid of the insulated screws 7.

The metal pieces are suitably made of highgrade magnetic iron or iron-cobalt alloys, in order that the greatest possible saving in ampere turns to' be made available, may be attained. On the contrary, the (magnetic) contact reluctance between the pole shoes and the said metal pieces is substantially diminished by the fact that the metal pieces are in contact with the pole shoes over a correspondingly larger surface.

What I claim is:

l. Electrodynamic acoustic apparatus comprising a magnet system having poles spaced from each other to provide an elongated narrow air gap, an elongated conductor positioned in said air gap, pole pieces positioned between said conductor and said poles and spaced from said conductor by narrow gaps whereby a slight twisting of said conductor will cause one end of said conductor to contact with one of said pole pieces and the other end to contact with the other of said pole pieces, screw means extending through said* pole pieces for securing said pole pieces to said poles, and means for electrically insulating said pole pieces from said poles and from said screws whereby said conductor will not be short circuited upon contact at opposite ends with said pole pieces.

2. Electrodynamic acoustic apparatus comprising a magnet system having poles spaced from each other to provide an elongated narrow air gap, an elongated conductor positioned in said air gap, pole pieces positioned between said conductor and said poles and spaced from said conductor by narrow gaps whereby a slight twisting of said conductor will cause one end of said conductor to contact with one of said pole pieces and the other end to contact with the other of said pole pieces, screw means extending through said pole pieces for securing said pole pieces to said poles, projections on said pole pieces along the edges thereof remote from the edges adjacent said conductor, said projections extending at right angles to the line of magnetic pull of said pole pieces toward each other, slots cut in said pole pieces in which said projections are adapted to fit, and thin layers of insulating material disposed between said pole pieces and said poles and between said pole pieces and said screws whereby said pole pieces are conductively isolated from the rest of the magnetic Structure and short Circuiting said conductor upon contact with said pole pieces is thereby prevented.

HANS NEUMANN. 

